Novel color-forming compounds and use thereof in imaging members and methods

ABSTRACT

There are described novel rhodamine color-forming compounds. The rhodamine color-forming compounds exhibit a first color when in a crystalline form and a second color, different from the first color, when in an amorphous form. Thermal imaging members containing these color-formers are also described.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of copending U.S. patentapplication Ser. No. 11/433,810, filed on May 12, 2006, entitled “NovelRhodamine Dyes” and of copending U.S. patent application Ser. No.11/433,808, filed May 12, 2006, entitled “Thermal Imaging Members andMethods”, the disclosures of which are hereby incorporated by referenceherein in their entirety.

This application is related to the following commonly assigned UnitedStates patent applications and patents, the disclosures of all of whichare hereby incorporated by reference herein in their entirety:

U.S. Pat. No. 6,801,233 B2 which describes and claims a thermal imagingsystem for use in the present invention;

U.S. Pat. No. 7,008,759 B2 which describes and claims color-formingcompositions for use in the present invention;

U.S. Pat. No. 7,176,161 B2 which describes and claims color-formingcompositions for use in the present invention;

U.S. Pat. No. 7,282,317 B2 which describes and claims color-formingcompositions for use in the present invention;

U.S. patent application Ser. No. 11/400,734, filed Apr. 6, 2006, whichdescribes and claims an imaging method for use in the present invention;

U.S. Pat. No. 7,408,563, which describes and claims an imaging methodfor use in the present invention;

U.S. patent application Ser. No. 12/022,955, filed Jan. 30, 2008,entitled “Printhead pulsing techniques for multicolor printers”; and

U.S. patent application Ser. No. 12/022,969, filed Jan. 30, 2008,entitled “Thermal Imaging Members and Methods”.

FIELD OF THE INVENTION

This invention relates to novel compounds and, more particularly, tocompounds which exhibit one color in the crystalline form and a second,different color in the liquid, or amorphous, form. Also described areimaging members and methods, including thermal imaging members andmethods, utilizing the compounds.

BACKGROUND OF THE INVENTION

The development of thermal printing heads (linear arrays ofindividually-addressable resistors) has led to the development of a widevariety of thermally-sensitive media. In some of these, known as“thermal transfer” systems, heat is used to move colored material from adonor sheet to a receiver sheet. Alternatively, heat may be used toconvert a colorless coating on a single sheet into a colored image, in aprocess known as “direct thermal” imaging. Direct thermal imaging hasthe advantage over thermal transfer of the simplicity of a single sheet.On the other hand, unless a fixing step is incorporated, direct thermalsystems are still sensitive to heat after thermal printing. If a stableimage is needed from an unfixed direct thermal system, the temperaturefor coloration must be higher than any temperature that the image islikely to encounter during normal use. A problem arises in that thehigher the temperature for coloration, the less sensitive the mediumwill be when printed with the thermal print head. High sensitivity isimportant for maximum speed of printing, for maximizing the longevity ofthe print head, and for energy conservation in mobile, battery-poweredprinters. As described in more detail below, maximizing sensitivitywhile maintaining stability is more easily achieved if the temperatureof coloration of a direct thermal medium is substantially independent ofthe heating time.

Thermal printing heads address one line of the image at a time. Forreasonable printing times, each line of the image is heated for aboutten milliseconds or less. Storage of the medium (prior to printing or inthe form of the final image) may need to be for years, however. Thus,for high imaging sensitivity, a high degree of coloration is required ina short time of heating, while for good stability a low degree ofcoloration is required for a long time of heating.

Most chemical reactions speed up with increasing temperature. Therefore,the temperature required for coloration in the short heating timeavailable from a thermal printing head will normally be higher than thetemperature needed to cause coloration during the long storage time.Actually reversing this order of temperatures would be a very difficulttask, but maintaining a substantially time-independent temperature ofcoloration, such that both long-time and short-time temperatures forcoloration are substantially the same, is a desirable goal that isachieved by the present invention.

There are other reasons why a time-independent coloration temperaturemay be desirable. It may, for example, be required to perform a secondthermal step, requiring a relatively long time of heating, afterprinting. An example of such a step would be thermal lamination of animage. The temperature of coloration of the medium during the timerequired for thermal-lamination must be higher than the aminationtemperature (otherwise the medium would become colorized duringlamination). It would be preferred that the imaging temperature behigher than the lamination temperature by as small a margin as possible,as would be the case for time-independent temperature of coloration.

Finally; the imaging system may comprise more than one color-forminglayer and be designed to be printed with a single thermal printing head,as described in the above-mentioned patent application Ser. No.10/151,432. In one embodiment of the imaging system, the topmostcolor-forming layer forms color in a relatively short time at arelatively high temperature, while the lower layer or layers form colorin a relatively long time at a relatively low temperature. An idealtopmost layer for this type of direct thermal imaging system would havetime-independent temperature of coloration.

Prior art direct thermal imaging systems have used several differentchemical mechanisms to produce a change in color. Some have employedcompounds that are intrinsically unstable, and which decompose to form avisible color when heated. Such color changes may involve a unimolecularchemical reaction. This reaction may cause color to be formed from acolorless precursor, the color of a colored material to change, or acolored material to bleach. The rate of the reaction is accelerated byheat. For example, U.S. Pat. No. 3,488,705 discloses thermally unstableorganic acid salts of triarylmethane dyes that are decomposed andbleached upon heating. U.S. Pat. No. 3,745,009 reissued as U.S. ReissuePat. No. 29,168 and U.S. Pat. No. 3,832,212 disclose heat-sensitivecompounds for thermography containing a heterocyclic nitrogen atomsubstituted with an —OR group, for example, a carbonate group, thatdecolorize by undergoing homolytic or heterolytic cleavage of thenitrogen-oxygen bond upon heating to produce an RO+ ion or RO′ radicaland a dye base or dye radical which may in part fragment further. U.S.Pat. No. 4,380,629 discloses styryl-like compounds that undergocoloration or bleaching, reversibly or irreversibly, via ring-openingand ring-closing in response to activating energies. U.S. Pat. No.4,720,449 describes an intramolecular acylation reaction that converts acolorless molecule to a colored form. U.S. Pat. No. 4,243,052 describespyrolysis of a mixed carbonate of a quinophthalone precursor that may beused to form a dye. U.S. Pat. No. 4,602,263 describes athermally-removable protecting group that may be used to reveal a dye orto change the color of a dye. U.S. Pat. No. 5,350,870 describes anintramolecular acylation reaction that may be used to induce a colorchange. A further example of a unimolecular color-forming reaction isdescribed in “New Thermo-Response Dyes: Coloration by the ClaisenRearrangement and Intramolecular Acid-Base Reaction Masahiko Inouye,Kikuo Tsuchiya, and Teijiro Kitao, Angew. Chem. Int. Ed. Engl. 31, pp.204-5 (1992).

In all of the above-mentioned examples, control of the chemical reactionis achieved through the change in rate that occurs with changingtemperature. Thermally-induced changes in rates of chemical reactions inthe absence of phase changes may often be approximated by the Arrheniusequation, in which the rate constant increases exponentially as thereciprocal of absolute temperature decreases (i.e., as temperatureincreases). The slope of the straight line relating the logarithm of therate constant to the reciprocal of the absolute temperature isproportional to the so-called “activation energy”. The prior artcompounds described above are coated in an amorphous state prior toimaging, and thus no change in phase is expected or described asoccurring between room temperature and the imaging temperature. Thus, asemployed in the prior art, these compounds exhibit stronglytime-dependent coloration temperatures. Some of these prior artcompounds are described as having been isolated in crystalline form.Nevertheless, in no case is there mentioned in this prior art any changein activation energy of the color-forming reaction that may occur whencrystals of the compounds are melted.

Other prior art thermal imaging media depend upon melting to triggerimage formation. Typically, two or more chemical compounds that reacttogether to produce a color change are coated onto a substrate in such away that they are segregated from one another, for example, asdispersions of small crystals. Melting, either of the compoundsthemselves or of an additional fusible vehicle, brings them into contactwith one another and causes a visible image to be formed. For example, acolorless dye precursor may form color upon heat-induced contact with areagent. This reagent may be a Bronsted acid, as described in “ImagingProcesses and Materials”, Neblette's Eighth Edition, J. Sturge, V.Walworth, A. Shepp, Eds., Van Nostrand Reinhold, 1989, pp. 274-275, or aLewis acid, as described for example in U.S. Pat. No. 4,636,819.Suitable dye precursors for use with acidic reagents are described, forexample, in U.S. Pat. No. 2,417,897, South African Patent 68-00170,South African Patent 68-00323 and Ger. Of fenlegungschrift 2,259,409.Further examples of such dyes may be found in “Synthesis and Propertiesof Phthalide-type Color Formers”, by Ina Fletcher and Rudolf Zink, in“Chemistry and Applications of Leuco Dyes”, Muthyala Ed., Plenum Press,New York, 1997. The acidic material may for example be a phenolderivative or an aromatic carboxylic acid derivative. Such thermalimaging materials and various combinations thereof are now well known,and various methods of preparing heat-sensitive recording elementsemploying these materials also are well known and have been described,for example, in U.S. Pat. Nos. 3,539,375, 4,401,717 and 4,415,633. U.S.Pat. Nos. 4,390,616 and 4,436,920 describe image forming memberscomprising materials similar to those of the present invention. Thematerials described therein are fluoran dyes for use in conjunction witha developer, and there is not a report of image formation upon meltingin the absence of a developer.

Prior art systems in which at least two separate components are mixedfollowing a melting transition suffer from the drawback that thetemperature required to form an image in a very short time by a thermalprint-head may be substantially higher than the temperature required tocolorize the medium during longer periods of heating. This difference iscaused by the change in the rate of the diffusion needed to mix themolten components together, which may become limiting when heat isapplied for very short periods. The temperature may need to be raisedwell above the melting points of the individual components to overcomethis slow rate of diffusion. Diffusion rates may not be limiting duringlong periods of heating, however, and the temperature at whichcoloration takes place in these cases may actually be less than themelting point of either individual component, occurring at the eutecticmelting point of the mixture of crystalline materials.

As the state of the art in imaging systems advances and efforts are madeto provide new imaging systems that can meet new performancerequirements, and to reduce or eliminate some of the undesirablecharacteristics of the known systems, it would be advantageous to havenew compounds which can be used as image-forming materials in imagingsystems, including thermal imaging systems.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide novel compounds.

Another object of the invention is to provide compounds which exhibit adifferent color when in the crystalline form than when in the amorphousform (which may be a liquid).

Yet another object of the invention is to provide imaging members andmethods, including thermal imaging members and methods, which utilizethe novel compounds.

The present invention provides novel rhodamine compounds that are usefulas image dyes in imaging systems. According to one aspect of theinvention there are provided novel color-forming compounds that arecolorless when in the crystalline form and exhibit the conjugatedrhodamine chromophore when in the amorphous form (which may be aliquid).

In one embodiment of the invention there are provided novelcolor-forming compounds that are represented by formula (I):

wherein:R₁-R₁₀ are alkyl or hydrogen;at least one of R₁₁, R₁₅, R₁₆ and R₂₀ is alkyl or halogen;at least one of R₁₁, R₁₃, R₁₅, R₁₆, R₁₈ and R₂₀ is fluorine;and R₁₁-R₂₀ are chosen from the group consisting of hydrogen, alkyl,substituted alkyl, halogen, alkoxy, and substituted carbonyl.

The conversion to the amorphous form can be carried out by applying heatto the compounds and therefore the compounds are useful in thermalimaging members used in thermal imaging methods. In such thermal imagingmethods thermal energy may be applied to the thermal imaging members byany of the techniques known in thermal imaging such as from a thermalprint head, a laser, a heated stylus, etc. In another embodiment, theconversion to the amorphous form may be effected by applying a solventfor the crystalline solid such as from an ink jet imaging apparatus toat least partially dissolve the crystalline material.

In yet another embodiment one or more thermal solvents, which arecrystalline materials, can be incorporated into the thermal imagingmember in close proximity to crystals of the compounds of the invention.The crystalline thermal solvent(s), upon being heated, melt and dissolveor liquefy, and thereby convert, at least partially, the crystallineimage-forming compound of the invention to the amorphous form, therebyforming an image.

The compounds of the invention may be incorporated in any suitablethermal imaging members. Typical suitable thermal imaging membersgenerally comprise a substrate carrying at least one image-forming layerincluding a compound of the invention in the crystalline form, which canbe converted, at least partially, to an amorphous form, the amorphousform having intrinsically a different color from the crystalline form.The thermal imaging member may be monochrome or multicolor. Thetemperature at which an image is formed in at least one of theimage-forming layers is preferred to be substantially time-independent.

Preferred thermal imaging members include those having the structuresdescribed in above-mentioned U.S. Pat. Nos. 6,801,233 and 7,176,161.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic, side sectional view of a three-color thermalimaging member according to the invention.

DEFINITIONS

The term “alkyl” as used herein refers to saturated straight-chain,branched-chain or cyclic hydrocarbon radicals. Examples of alkylradicals include, but are not limited to, methyl, ethyl, propyl,isopropyl, n-butyl, tert-butyl, neopentyl, n-hexyl, cyclohexyl, n-octyl,n-decyl, n-dodecyl and n-hexadecyl radicals.

The term “alkenyl” as used herein refers to unsaturated straight-chain,branched-chain or cyclic hydrocarbon radicals. Examples of alkenylradicals include, but are not limited to, allyl, butenyl, hexenyl andcyclohexenyl radicals.

The term “alkynyl” as used herein refers to unsaturated hydrocarbonradicals having at least one carbon-carbon triple bond. Representativealkynyl groups include, but are not limited to, ethynyl, 1-propynyl,1-butynyl, isopentynyl, 1,3-hexadiynyl, n-hexynyl, 3-pentynyl,1-hexen-3-ynyl and the like.

The terms “halo” and “halogen”, as used herein, refer to an atomselected from fluorine, chlorine, bromine and iodine.

The term “aryl”, as used herein, refers to a mono-, bicyclic ortricyclic carbocyclic ring system having one, two or three aromaticrings including, but not limited to, phenyl, naphthyl, anthryl, azulyl,tetrahydronaphthyl, indanyl, indenyl and the like.

The term “heteroaryl”, as used herein, refers to a cyclic aromaticradical having from five to ten ring atoms of which one ring atom isselected from S, O and N; zero, one or two ring atoms are additionalheteroatoms independently selected from S, O and N; and the remainingring atoms are carbon, the radical being joined to the rest of themolecule via any of the ring atoms, such as, for example, pyridinyl,pyrazinyl, pyrimidinyl, pyrrolyl, pyrazolyl, imidazolyl, thiazolyl,oxazolyl, isooxazolyl, thiadiazolyl, oxadiazolyl, thiophenyl, furanyl,quinolinyl, isoquinolinyl, and the like.

The term “heterocycloalkyl”, as used herein, refers to a non-aromatic3-, 4-, 5-, 6- or 7-membered ring or a bi- or tri-cyclic groupcomprising fused six-membered rings having between one and threeheteroatoms independently selected from oxygen, sulfur and nitrogen,wherein (i) each 5-membered ring has 0 to 1 double bonds and each6-membered ring has 0 to 2 double bonds, (ii) the nitrogen and sulfurheteroatoms may optionally be oxidized, (iii) the nitrogen heteroatommay optionally be quaternized, and (iv) any of the above heterocyclicrings may be fused to a benzene ring. Representative heterocyclesinclude, but are not limited to, pyrrolidinyl, pyrazolinyl,pyrazolidinyl, imidazolinyl, imidazolidinyl, piperidinyl, piperazinyl,oxazolidinyl, isoxazolidinyl, morpholinyl, thiazolidinyl,isothiazolidinyl, and tetrahydrofuryl.

The term “carbonyl” as used herein refers to a carbonyl group, attachedto the parent molecular moiety through the carbon atom, this carbon atomalso bearing a hydrogen atom, or in the case of a “substituted carbonyl”a substituent as described in the definition of “substituted” below.

The term “acyl” as used-herein refers to groups containing a carbonylmoiety. Examples of acyl radicals include, but are not limited to,formyl, acetyl, propionyl, benzoyl and naphthyl.

The term “alkoxy”, as used herein, refers to a substituted orunsubstituted alkyl, alkenyl or heterocycloalkyl group, as previouslydefined, attached to the parent molecular moiety through an oxygen atom.Examples of alkoxy radicals include, but are not limited to, methoxy,ethoxy, propoxy, isopropoxy, n-butoxy, tert-butoxy, neopentoxy andn-hexoxy.

The term “aryloxy” as used herein refers to a substituted orunsubstituted aryl or heteroaryl group, as previously defined, attachedto the parent molecular moiety through an oxygen atom. Examples ofaryloxy include, but are not limited to, phenoxy, p-methylphenoxy,naphthoxy and the like.

The term “alkylamino”, as used herein, refers to a substituted orunsubstituted alkyl, alkenyl or heterocycloalkyl group, as previouslydefined, attached to the parent molecular moiety through a nitrogenatom. Examples of alkylamino radicals include, but are not limited to,methylamino, ethylamino, hexylamino and dodecylamino.

The term “arylamino”, as used herein, refers to a substituted orunsubstituted aryl or heteroaryl group, as previously defined, attachedto the parent molecular moiety through a nitrogen atom.

The term “substituted” as used herein in phrases such as “substitutedalkyl”, “substituted alkenyl”, “substituted aryl”, “substitutedheteroaryl”, “substituted heterocycloalkyl”, “substituted carbonyl”,“substituted alkoxy”, “substituted acyl”, “substituted amino”,“substituted aryloxy”, and the like, refers to independent replacementof one or more of the hydrogen atoms on the substituted moiety withsubstituents independently selected from, but not limited to, alkyl,alkenyl, heterocycloalkyl, alkoxy, aryloxy, hydroxy, amino, alkylamino,arylamino, cyano, halo, mercapto, nitro, carbonyl, acyl, aryl andheteroaryl groups.

DETAILED DESCRIPTION OF THE INVENTION

Compounds in the crystalline state commonly have properties, includingcolor, that are very different from those of the same compounds in anamorphous form. In a crystal, a molecule is typically held in a singleconformation (or, more rarely, in a small number of conformations) bythe packing forces of the lattice. Likewise, if a molecule can exist inmore than one interconverting isomeric form (such forms being referredto in the art as “tautomers”), only one of such isomeric forms iscommonly present in the crystalline state. In the amorphous state or insolution, on the other hand, the compound may explore its wholeconformational and isomeric space, and only a small proportion of thepopulation of individual molecules of the compound may at any one timeexhibit the particular conformation or isomeric form adopted in thecrystal. Compounds of the present invention exhibit tautomerism in whichat least one tautomeric form is colorless, and at least anothertautomeric form is colored. The crystalline form of compounds of thepresent invention comprises predominantly the colorless tautomer.

According to the invention, there have been provided moleculesexhibiting tautomerism in which at least one tautomeric form iscolorless, and at least another tautomeric form is colored.Crystallization of the equilibrating mixture of the two tautomeric formsin solution is carried out so as to produce colorless crystals. Thesolvent chosen to perform the crystallization will typically be one ofsuch polarity (and other chemical properties, such as hydrogen-bondingability) that the pure colorless crystal form is favored, either in theequilibrium between the colorless and colored forms in solution, or inhaving lower solubility in the solvent than the colored form. The choiceof solvent is usually determined empirically for a particular mixture oftautomers.

As discussed in more detail below, the substituents of the preferredcompounds of the present invention are chosen so as to enable thecolorless tautomer to be prepared in a practical manner in the form ofcolorless crystals.

Upon conversion of the pure crystalline colorless form to the amorphousform, the equilibrium between the two tautomers is re-established. Theproportion of the amorphous material that is colored (i.e., theproportion that is in the colored tautomeric form) may vary, but ispreferably at least about 10%. The proportion (expressed as apercentage) of the total amorphous material that is colored (in theabsence of any other materials) is hereinafter referred to as the “%coloration” of the color-forming compound. The substituents of thepreferred compounds of the present invention are chosen so as tomaximize the % coloration without sacrificing the ability to formcolorless crystals in a practical manner.

The colored and colorless tautomeric forms of the molecules of thepresent invention must meet certain criteria for image quality andpermanence. The colorless form, which is preferably the crystallineform, should have minimal visible absorption. It should be stable tolight, heating below the melting point, humidity, and otherenvironmental factors such as ozone, oxygen, nitrogen oxides,fingerprint oils, etc. These environmental factors are well known tothose skilled in the imaging art. The colored, amorphous form should bestable also to the above-mentioned conditions, and in addition shouldnot recrystallize to the colorless form under normal handling conditionsof the image. The colored form should have a spectral absorptionappropriate for digital color rendition. Typically, the colored formshould be yellow (blue-absorbing), magenta (green-absorbing), cyan (redabsorbing), or black, without undue absorption in an unintended spectralregion. For nonphotographic applications, however, it may be requiredthat the colored form not be one of the subtractive primary colors, butrather a particular spot color (for example, orange, blue, etc.).

The novel compounds of the present invention are most useful as magentacolor-formers, i.e., materials absorbing light in the green region ofthe electromagnetic spectrum. The wavelength of maximum absorption forsuch compounds is ideally between 540 and 550 nm, and the shape of theabsorption curve is preferably such that minimal blue light (wavelengthsbelow about 500 nm) and red light (wavelengths above about 600 nm) areabsorbed.

The melting points of the compounds determine how the compounds may beused in thermal imaging members. For example, in a three-color thermalimaging member such as is disclosed in the above-mentioned U.S. Pat. No.6,801,233 B2, the layer that is imaged in the shortest time, but withthe highest temperature at the surface of the imaging member, typicallyhas an activation temperature above 200° C. The layer that is imagedwith an intermediate surface temperature, for an intermediate time,typically has an activation temperature of about 150-180° C. The layerthat is imaged with the lowest surface temperature, for the longesttime, typically has an activation temperature of about 90-130° C.

As discussed in more detail below, color-forming molecules of thepresent invention whose activation temperatures are not ideal, but whichotherwise meet the requirements for incorporation into a thermal imagingmember, may be used in conjunction with thermal solvents (crystallinecompounds that, when melted, dissolve the color-forming molecule of thepresent invention). In such cases, the activation temperature may bedetermined by the melting point of the thermal solvent.

Another important property of the color-forming compounds of the presentinvention is the glass transition temperature, Tg. In order for theimage formed by the amorphous color-former to be stable againstrecrystallization back to the crystalline form, preferably the glasstransition temperature (T_(g)) of the amorphous mixture of thecolor-former (if used alone) should be higher than any temperature thatthe final image must survive. Typically, it is preferred that the T_(g)of the amorphous, colored material be at least about 50° C., and ideallyabove about 60° C.

A first embodiment of the present invention is a compound whosecolorless tautomer is represented by formula (I) as described above.Representative compounds according to the invention are those of formula(I) shown in Table I, below. The dyes are listed in the order ofdecreasing % coloration in the amorphous form.

TABLE I R1- R10, Dye R12, # R15 R11 R13 R14 R16 R17 R18 R19 R20 1 H Me FH Me H OMe H H 2 H Me F H Me H H H Me 3 H Me Me H Et H H H Me 4 H Me F HEt H H H H 5 H Me F H Me H Me H H 6 H F Me H Me H F H H 7 H Me F H Me HH Me H 8 H Me F H Me F H H H 9 H Me F H Me H H H H 10 H Me F H Me H H FH 11 H F Me H H H F H H 12 H Me F H Me H F H H 13 H F F H Me H H Me H 14H Me OMe H Et H H H Me 15 H F Me H Me H OMe H H 16 H F F H Me H H H Me17 H F Me H Me H Me H H 18 H Me F H Me H CONPr2 H H 19 H F Me H F H Me HH 20 H F Me H i-Pr H H H H 21 H F F H i-Pr H H H H 22 H F F H Et H H H H23 H Me F H F H H H H 24 H F Me H Me H H Me H 25 H F Me H Et H H H H 26H F H H Me H H Me H 27 H F Me H Me H H H Me 28 H F H H Me H H H Me 29 HF Me H Me H H H H 30 H F H H i-Pr H H H H 31 H F H H Me H Cl H H 32 H FH H Me H H H H 33 H Me OMe H OMe H H H H 34 H F F H Me H H F H 35 H F MeH Me F H H H 36 H Me F H OMe H H H H 37 H F Me H Me H H F H 38 H F H HMe H H F H 39 H F H H F Me H H H 40 H Me Me H OMe H H H H 41 H F Me H FH H H H 42 H F H H F H H H H 43 H F Me H OMe H H H H 44 H Me F H OEt H HH H 45 H F Me H OEt H H H H 46 H F H H OEt H H H H 47 H Cl Me H Cl H MeH H

Some relevant physical properties of Dyes 1-47 are shown below in TableII. In some instances a property was not measured, as indicated by N/Ain the Table.

TABLE II Heat of Amorphous Dye # λ_(max(film)) Color MP (° C.) Tg (° C.)Fusion (J/g) coloration (%) Crystallinity 1 548 Purple 218.38 115.7474.09 80% Amorphous 2 544 Magenta N/A N/A N/A 70% Amorphous 3 552 N/AN/A N/A N/A 58% Amorphous 4 546 Pink 161.25 106.14 45.09 53% Crystalline5 546 Pink 237.77 116.77 69.53 52% Crystalline 6 544 Purple 249.48101.01 72.65 51% Crystalline 7 546 Pink 212.35 115.29 59.6 50%Crystalline 8 544 Magenta N/A N/A N/A 47% Amorphous 9 552 Pink 235.27113.72 64 47% Crystalline 10 544 Magenta N/A N/A N/A 45% Amorphous 11554 Purple >260 N/A N/A 45% Crystalline 12 544 Magenta 221.5 115.8562.53 43% Crystalline 13 546 Pink 225.17 107.5 74.12 42% Crystalline 14548 N/A N/A N/A N/A 41% Crystalline 15 550 Red 234.43 108.26 71.46 41%Crystalline 16 542 Pink 176.43 123.78 45.61 40% Crystalline 17 548 Red247.16 109.33 86.99 39% Crystalline 18 544 N/A 230 N/A N/A 36%Crystalline 19 546 Pink 261.88 104.27 88.1 36% Crystalline 20 548 Pink203 101.41 65.04 36% Crystalline 21 544 Pink 213.8 91.02 66.18 35%Crystalline 22 544 Pink 172.60 98.84 52.81 35% Crystalline 23 546 Pink218 106.31 68.23 33% Crystalline 24 550 Pink 199.11 108.73 62.13 33%Crystalline 25 550 Red 208.85 92.92 66.94 29% Crystalline 26 546 White210.69 104.64 72.32 28% Crystalline 27 546 Pink 121.03, 173.32 124.3914.36, 39.15 26% Solvate 28 542 Pink 133.47 124.83 67.43 24% Crystalline29 546 Pink 222.41 107.68 78.5 23% Crystalline 30 548 Pink 102.44 88.28101.5 23% Solvate 31 544 Pink 245.42 109.18 80.48 19% Crystalline 32 546White 192.37 105.11 62.39 18% Crystalline 33 554 Pink 219.1 104.85 74.8317% Crystalline 34 540 White 210.35 103.89 68.9 16% Crystalline 35 544Magenta N/A N/A N/A 16% Amorphous 36 550 Pink 151.55 108.22 35.85 16%Crystalline 37 546 Pink 209.38 103.69 64.65 15% Crystalline 38 544 White239.48 104.02 85.25 14% Crystalline 39 544 Magenta N/A N/A N/A 13%Amorphous 40 554 Pink 198.43 106.89 56.31 13% Crystalline 41 546 Pink243.93 109.88 78.08  9% Crystalline 42 544 Magenta 235 N/A N/A  7%Crystalline 43 556 Pink 98.56 99.56 63.75  7% Solvate 44 548 Pink 177.0798.32 50.95  6% Crystalline 45 560 White 180.6 93.56 66.69  0%Crystalline 46 N/A White 196.52 92.88 65.82  0% Crystalline 47 N/AMagenta 177.47, 208.06 104 8.18, 31.89 N/A Solvate

In Table II, the term “color” refers to the isolated crystals when it isindicated that the compound is crystalline. When such crystals aredescribed as “pink”, they may be appropriate for incorporation into athermal imaging member, since the pink coloration may result from slightresidual amorphous material that may become invisible when the crystalsare incorporated into a thin film. Typically, a color-forming layer in athermal imaging member of the present invention comprises about 0.1-1g/m² of a color-forming compound of the present invention, in the formof crystals less than about 1 micrometer in diameter.

In some cases, the crystals that are formed from color-forming compoundsare solvates, as indicated in Table II. Solvate crystals may exhibitinferior stability to crystals of the pure material, and may bedifficult to obtain in a reproducible manner. It is preferred that thecrystalline form of compounds of the present invention comprise crystalsof the pure material, not including any of the solvent ofcrystallization, when these materials are intended for incorporationinto a thermal imaging member.

The present inventors have found that it is generally impossible toobtain colorless, crystalline materials from compounds of formula (I)(i.e., compounds in which both nitrogen atoms bonded to the xanthenenucleus bear one hydrogen atom) unless at least one of R₁₁, R₁₅, R₁₆ andR₂₀ (the ortho substituents on the phenyl rings) is not hydrogen, andpreferably alkyl or halogen (preferably fluorine) it is hypothesizedthat the presence of ortho substituents bulkier than hydrogen impedeshydrogen-bonding association between color-forming molecules that favorsthe colored tautomer and therefore makes the preparation of colorlesscrystals difficult (although this is a hypothesis only and not intendedto limit the scope of the invention in any way).

Colorless compounds of formula (I) (a tautomeric form also referred toherein as the “closed form”) may also exist as a colored tautomerillustrated by formula (II) (also referred to herein as the “openform”):

wherein R₁-R₂₀ are as defined above with respect to formula (I).

Compounds of formula (II) typically exhibit maximum absorption of lightin the range of 500-600 nm. As such, these compounds are typicallymagenta dyes. The quality of the magenta chromophore is difficult topredict a priori in the current state of the imaging art, and moreovermay be dependent upon the environment of the compound. Factors such asthe dielectric constant and pH of the environment may profoundly affectthe chromophore, both by direct perturbation and by facilitatingaggregation of more than one dye molecule, as is well known in the art.

Nevertheless, it been found that, in the case where the compounds of thepresent invention are intended as magenta dyes in a photographicapplication, the presence of a single ortho substituent bulkier thanhydrogen on at least one of the phenyl rings results in a sharperabsorption peak and a superior magenta chromophore than would be thecase where all four ortho substituents on the phenyl rings are hydrogen.It is not preferred that both ortho substituents on a particular phenylring be bulkier than hydrogen, however, since in this case it is thoughtthat steric hindrance may cause twisting of the phenyl ring out of theplane of the xanthene chromophore, resulting in a perturbation to thechromophore.

The present inventors have also found that it is difficult to predictthe degree of amorphous coloration from the structure of a compound offormula (I). Nevertheless, in general, when each phenyl ring bears anortho substituent that is a hydrogen bond acceptor (such as fluorine oralkoxy) the degree of amorphous coloration has been found to be low(see, for example, dyes 39, 41, 42, 43, 45 and 46 in Tables I and II).

If neither of the phenyl rings bears an ortho substituent that is ahydrogen bond acceptor, conversely, the degree of amorphous colorationis typically high (see, for example, dyes 1-5). In such cases, however,it may be difficult to maintain the material in the colorless,crystalline form, if this can even be prepared at all.

It is therefore especially preferred for only one of the two phenylrings to bear an ortho substituent that is a hydrogen bond acceptor, andpreferably this substituent is fluorine. Stated otherwise, it isespecially preferred that exactly one of substituents R₁₁, R₁₅, R₁₆ andR₂₀ be fluorine.

To form a direct thermal imaging system, the crystalline, colorless formof the compounds of the invention is made into a dispersion in a solventin which the compound is insoluble or only sparingly soluble, by any ofthe methods known in the art for forming dispersions. Such methodsinclude grinding, attriting, etc in order to reduce the particle size ofthe crystals. The particular solvent chosen will depend upon theparticular crystalline material. Solvents that may be used includewater, organic solvents such as hydrocarbons, esters, alcohols, ketones,nitriles, and organic halide solvents such as chlorinated andfluorinated hydrocarbons. The dispersed crystalline material may becombined with a binder, which may be polymeric. Suitable binders includewater-soluble polymers such as poly(vinyl alcohol),poly(vinylpyrollidone) and cellulose derivatives, water-dispersedlatices such as styrene/butadiene or poly(urethane) derivatives, oralternatively hydrocarbon-soluble polymers such as polyethylene,polypropylene, copolymers of ethylene and norbornene, and polystyrene.This list is not intended to be exhaustive, but is merely intended toindicate the breadth of choice available for the polymeric binder. Thebinder may be dissolved or dispersed in the solvent.

Following preparation of the dispersion of the compound of the presentinvention, and optional addition of a polymeric binder, the resultantfluid is coated onto a substrate using any of the techniques well-knownin the coating art. These include slot, gravure, Mayer rod, roll,cascade, spray, and curtain coating techniques. The image-forming layerso formed is optionally overcoated with a protective layer or layers.

According to the present invention, the compounds of formula (I) may beincorporated into any thermal imaging members and used in any thermalimaging methods, including direct thermal imaging members and thermaltransfer imaging members and methods.

In one embodiment of the present invention, as discussed above, one ormore thermal solvents, which are, crystalline materials, can beincorporated in the thermal imaging member. The crystalline thermalsolvent(s), upon being heated, melt and thereafter dissolve or liquefythe crystalline color-forming material of formula (I), therebyconverting it to the amorphous form and providing a color change (i.e.,an image). Thermal solvents may be advantageously used when it isrequired for a color-forming layer in a direct thermal imaging member tohave an activation temperature (the temperature at which color is formedor at which color changes) that is lower than the melting point of thecompound of formula (I). The melting point of the thermal solvent,rather than that of the compound of formula (I), may in such a caseestablish the activation temperature of a color-forming layer.

It will be clear to one of ordinary skill in the art that the activationtemperature of a color-forming layer that comprises a mixture ofcrystalline materials may be different from the melting points of any ofthe individual components. A eutectic mixture of two crystallinecomponents, for example, melts at a lower temperature than either of thecomponents in isolation. Conversely, if the rate of solubilization ofthe compound of formula (I) in the molten thermal solvent is slow, theactivation temperature of the mixture may be higher than the meltingpoint of the thermal solvent. Recall that the activation temperature ofa mixture of a compound of formula (I) and a thermal solvent is thetemperature at which the color of the mixture changes, i.e., thetemperature at which a sufficient amount of the compound of formula (I)dissolves in the molten thermal solvent to provide a visible colorchange. It will be clear from the above discussion that the activationtemperatures of mixtures of compounds of formula (I) and thermalsolvents may be dependent upon the rate of heating. For these reasons,in the design of thermal imaging members of the present inventiondetermination of the actual activation temperature of a composition ispreferred to be carried out experimentally.

Any suitable thermal solvents may be incorporated in the thermal imagingmembers of the invention. Suitable thermal solvents include, forexample, aromatic and aliphatic ethers, diethers and polyethers,alkanols containing at least about 12 carbon atoms, alkanediolscontaining at least about 12 carbon atoms, monocarboxylic acidscontaining at least about 12 carbon atoms, esters and amides of suchacids, aryl amides, especially benzanilides, aryl sulfonamides andhydroxyalkyl-substituted arenes.

Specific preferred thermal solvents include: 1,2-diphenoxyethane,1,2-bis(4-methylphenoxy)ethane, tetradecan-1-ol, hexadecan-1-ol,octadecan-1-ol, dodecane-1,2-diol, hexadecane-1,16-diol, myristic acid,palmitic acid, stearic acid, methyl docosanoate,1,4-bis(hydroxymethyl)benzene, diaryl sulfones such as diphenylsulfone,4,4′-dimethyldiphenylsulfone, phenyl p-tolylsulfone and4,4′-dichlorodiphenylsulfone, and p-toluenesulfonamide.

Particularly preferred thermal solvents are ethers such as1,2-bis(2,4-dimethylphenoxy)ethane,1,4-bis(4-methylphenoxymethyl)benzene,bis(4-phenoxyphenoxymethyl)benzene and 1,4-bis(benzyloxy)benzene.

It is possible that the dissolution of the compounds of formula (I) by athermal solvent may lead to an amorphous form (in which the compound isdissolved in the amorphous thermal solvent) in which the proportion ofthe open, colored form is different from the proportion that would bepresent in the amorphous form resulting from melting the compound offormula (I) alone (i.e., without interaction with the thermal solvent).In particular, the proportion of the open, colored form of the compoundin the amorphous material may be enhanced by use of hydrogen-bonding oracidic thermal solvents. Materials that increase the proportion of thecolor-forming material that is in the open, colored form are hereinafterreferred to as “developers”. It is possible that the same compound mayserve the function of thermal solvent and developer. Preferreddevelopers include phenols such as4,4′-butylidenebis[2-(1,1-dimethylethyl)-5-methyl-phenol],2,2′-methylenebis(6-tert-butyl-4-methylphenol),2,2′-methylenebis(6-tert-butyl-4-ethylphenol),2,2′-ethylidenebis(4,6-di-tert-butylphenol),bis[2-hydroxy-5-methyl-3-(1-methylcyclohexyl)phenyl]methane,1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate,2,6-bis[[3-(1,1-dimethylethyl)-2-hydroxy-5-methylphenyl]methyl]-4-methylphenol,2,2′-butylidenebis[6-(1,1-dimethylethyl)-4-methylphenol,2,2′-(3,5,5-trimethylhexylidene)bis[4,6-dimethyl-phenol],2,2′-methylenebis[4,6-bis(1,1-dimethylethyl)-phenol,2,2′-(2-methylpropylidene)bis[4,6-dimethyl-phenol],1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate,2,2′-thiobis(4-tert-octylphenol), and3-tert-butyl-4-hydroxy-5-methylphenyl sulfide.

In order for the image formed by the amorphous color-former to be stableagainst recrystallization back to the crystalline form, preferably theglass transition temperature (Tg) of the amorphous mixture of thecolor-former and any thermal solvent should be higher than anytemperature that the final image must survive. Typically, it ispreferred that the Tg of the amorphous, colored material be at leastabout 50° C., and ideally above about 60° C. In order to ensure that theTg is sufficiently high for a stable image to be formed, materialshaving a high Tg may be added to the color-forming composition. Suchmaterials, hereinafter referred to as “stabilizers”, when dissolved inthe amorphous mixture of color-former, optional thermal solvent, andoptional developer, serve to increase the thermal stability of theimage.

Preferred stabilizers have a Tg that is at least about 60° C., andpreferably above about 80° C. Examples of such stabilizers are theaforementioned1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate (Tg123° C.) and 1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane (Tg101° C.). The stabilizer molecule may also serve as a thermal solvent oras a developer.

For example, the color-forming material may itself have a meltingtemperature above the desired temperature for imaging, and a Tg (in theamorphous form) of about 60° C. In order to produce a color-formingcomposition melting at the desired temperature, it may be combined witha thermal solvent that melts at the desired temperature for imaging. Thecombination of thermal solvent and color-forming material may, however,have a Tg that is substantially lower than 60° C., rendering the(amorphous) image unstable. In this case, a stabilizer such as1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl) isocyanurate maybe added, to raise the Tg of the amorphous material. In addition, theremay be provided a developer, for example, a phenolic compound such as2,2′-ethylidenebis(4,6-di-tert-butylphenol), in order to increase theproportion of the color-forming material that is in the colored form inthe amorphous phase.

Preferably the color-forming compound of the present invention, the(optional) thermal solvent, the (optional) developer and the (optional)stabilizer are each predominantly in their crystalline forms prior toimaging. By “predominantly” is meant at least about 50% and preferablymore than that. During imaging, at least one of these materials meltsand an amorphous mixture of the materials is formed. The amorphousmixture is colored, whereas the crystalline starting materials are not.

The temperature range over which melting (and therefore coloration)occurs should be as narrow as possible, especially in the case that thecompounds of the present invention are incorporated into a thermalimaging member capable of forming full-color images. It is preferredthat the temperature range of melting (as measured by differentialscanning calorimetry) of a color-forming composition comprising acompound of the present invention be less than 15° C. as measured at thehalf height of the peak, and preferably less than 10° C. measured athalf height.

As mentioned above, color-forming compounds of the present invention aremost appropriate for affording magenta coloration. In one preferredthermal imaging member of the present invention the magentacolor-forming layer is the middle of three color-forming layers, and hasan ideal activation temperature onset of between 145° C. and 160° C.

Two preferred color-forming compositions of the present invention are:

a. a mixture of Dye 23 of the present invention (1 part by weight),1,4-bis(4-methylphenoxymethyl)benzene (a thermal solvent, 5 parts byweight), 4,4′-butylidenebis[2-(1,1-dimethylethyl)-5-methyl-phenol] (adeveloper, 2 parts by weight),1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate (astabilizer, 0.5 parts by weight), and a polymeric binder, for example,poly(vinyl alcohol) (2-5 parts by weight) (onset of melting 149° C.,range of melting measured at half height 9° C.); andb. a mixture of Dye 23 of the present invention (1 part by weight),1,4-bis(4-phenoxyphenoxymethyl)benzene (a thermal solvent, 5 parts byweight), 4,4′-butylidenebis[2-(1,1-dimethylethyl)-5-methyl-phenol] (adeveloper, 2 parts by weight),1,3,5-tris(2,6-dimethyl-3-hydroxy-4-tert-butylbenzyl)isocyanurate (astabilizer, 0.5 parts by weight), and a polymeric binder, for example,poly(vinyl alcohol) (2-5 parts by weight) (onset of melting 152.5° C.,range of melting measured at half height 6.58° C.).

It is possible that one of the components in the amorphous, coloredmixture may recrystallize after the image has been formed. It isdesirable that such recrystallization not change the color of the image.In the case that a color-former, thermal solvent, developer andstabilizer are used, the thermal solvent may typically recrystallizewithout greatly affecting the color of the image.

The substituents on the compounds of formula (I) are preferably chosento minimize the water solubility of the compounds and facilitate theformation of a colorless form in non-polar, non-protic solvents. This isbecause the manufacture of a thermal imaging member of the presentinvention typically involves an aqueous coating process. Were thecompound of formula (I) to dissolve appreciably in water (the coatingsolvent), the coloration that is intended to occur when heating thethermal imaging member itself would occur prematurely duringmanufacture. On the other hand, the thermal solvents, when used, aretypically non-polar, non-protic solvents, and are intended to dissolvethe compounds of formula (I).

Yet another consideration is the stability of the image formed by thecompound of formula (I). When used in a direct thermal imaging member,the colorless form of the compound (formula (I) itself) and the coloredform of the compound (formula (II)) each must be stable, since in suchimaging members the material is present both in colored and uncoloredregions. In particular, the forms represented by formulas I and II mustbe stable to ultraviolet light and to oxidation in the presence orabsence of light of any wavelength. The present inventors have foundthat the light stability of the colorless form of compounds of thepresent invention is maximized when each nitrogen atom attached to thexanthene nucleus bears an aryl group and a hydrogen atom, as shown informula (I). Note that some compounds of the prior art bear alkylsubstituents on at least one of these nitrogen atoms. Such alkyl groupsmay be prone to removal by photo-oxidation, leading to coloration of thecolorless crystals in the presence of light and oxygen.

A particularly preferred compound of formula (I), meeting all theabove-mentioned requirements, is Dye 23. As shown in Example IX, below,Dye 23 exhibits the best light stability in the colorless crystallineform of the compounds tested.

The compounds used according to the invention may be prepared bysynthetic processes which are known to those skilled in the art,particularly in view of the state of the art in organic syntheticprocesses, and the present disclosure and specific preparatory examplesprovided below herein.

Generally, symmetrical rhodamine dyes can be prepared in one step from3′,6′-dichlorofluorans by reacting two equivalents of an aromatic oraliphatic amine as described in U.S. Pat. No. 4,602,263, GB2311075 andDE81056.

Alternatively, the unsymmetrical rhodamines can be prepared by use of analternate synthetic pathway in which one equivalent of an aniline orother aromatic amine is reacted selectively with the3′,6′-dichlorofluoran using aluminum chloride as a catalyst to produce3′-chloro-6′-N-arylfluorans. These products may be isolated andpurified, or may be directly reacted with a second aromatic amine. Zincchloride or another Lewis acid may be used as the catalyst for thesecond addition. DE139727 describes the selective addition of anilinesto 3′,6′-dichlorofluorans to produce 3′-chloro-6′-arylaminofluoransusing a mixture of zinc chloride and zinc oxide at 160° C.

Unsymmetrical rhodamines can also be made from 2-benzoyl benzoic acidderivatives by condensation with 3-arylamino phenols as described inChemistry and Applications of Leuco Dyes, pp. 180-191 R. Muthyala, Ed.,Plenum Press, New York and London, 1997 and also U.S. Pat. Nos.4,390,616 and 4,436,920.

To optimize the chromophore, melting point, degree of coloration, lightstability and solubility of the dyes in this application a variety ofaromatic amines are utilized.

The aromatic amines used in this application are typically commerciallyavailable, or may be synthesized by reduction of the corresponding nitrocompounds.

3′,6′-dichlorofluoran is synthesized from fluorescein using thionylchloride and dimethylformamide in a variation of the method of Hurddescribed in the Journal of the Amer. Chemical Soc. 59, 112 (1937).

Careful recrystallization of the color-forming materials of formula (I)from solvent mixtures such as heptanes/acetone, water/acetone,heptanes/ethyl acetate, heptanes/toluene, or single solvents such astoluene produces colorless crystalline material which is preferred foruse in thermal imaging members.

Examples of the preparation of preferred compounds of the presentinvention are given below.

Referring now to FIG. 1, a preferred thermal imaging member 10 accordingto the invention is shown in schematic form. All layers were coated fromaqueous fluids which contained small amounts of a coating aid, ZonylFSN, available from Dupont Co., Wilmington, Del.

The substrate 12 is a filled, white, oriented polypropylene base ofthickness about 200 microns, FPG200, available from Yupo CorporationAmerica, Chesapeake, Va. 23320.

An adhesion-promoting layer 14 overlies the substrate 12, composed ofthe CP655 (a latex available from Dow Chemical Co., Midland, Mich., 48%by weight), CP692 (a latex available from Dow Chemical Co., Midland,Mich., 31% by weight) and POVAL MP103 (a fully hydrolyzed polyvinylalcohol) available from Kuraray America, Inc., New York, N.Y., 21% byweight). This layer has a coverage of 7.5 g/m2.

Overlying the adhesion-promoting layer 14 is an oxygen barrier layer 16composed of the above-mentioned POVAL MP103 (89.3% by weight) andglyoxal (a crosslinker, 10.7% by weight). This layer has a coverage of1.2 g/m2.

Overlying the oxygen barrier layer 16 is a cyan color-forming layer 18composed of a cyan color-former having melting point 210° C., Dye X ofcopending U.S. patent application Ser. No. 12/022,969 (1 part byweight), 1,2-bis(2,4-dimethylphenoxy)ethane (a thermal solvent havingmelting point 112° C., coated as an aqueous dispersion of crystalshaving average particle size under 1 micron, 6 parts by weight), aphenolic antioxidant/developer (Anox 29, having melting point 161-164°C., available from Chemtura, Middlebury, Conn., coated as an aqueousdispersion of crystals having average particle size under 1 micron, 1part by weight), Lowinox 1790 (a second phenolic antioxidant/stabilizer,available from Chemtura, Middlebury, Conn. coated as an aqueousdispersion of crystals having average particle size under 1 micron, 1.5parts by weight), a binder (poly(vinyl alcohol), Celvol 205, availablefrom Celanese, Dallas, Tex., 7 parts by weight) and glyoxal (0.42 partsby weight). This layer has a coverage of 3.35 g/m2.

Overlying the cyan color-forming layer 18 is a barrier layer 20 thatcontains a fluorescent brightener. This layer is composed of theabove-mentioned POVAL MP103 (82% by weight), glyoxal (8% by weight) andLeucophor BCF P115 (a fluorescent brightener, available from ClariantCorp., Charlotte, N.C., 10% by weight). This layer has a coverage of 2g/m2.

Overlying the barrier layer 20 is a thermally-insulating interlayer 22composed of the above-mentioned CP692 (93% by weight) and theabove-mentioned POVAL MP103 (7% by weight). This layer has a coverage of27.5 g/m2.

Overlying the thermally-insulating interlayer 22 is a barrier layer 24composed the above-mentioned POVAL MP103 (94% by weight) and glyoxal (acrosslinker, 6% by weight). This layer has a coverage of 1.5 g/m2.

Overlying the barrier layer 24 is a magenta color-forming layer 26,composed of a magenta color-former, Dye 23 of the present invention (1part by weight); an a phenolic ether,1,4-bis[(4-methylphenoxy)methyl]-benzene, (melting point 172° C., coatedas an aqueous dipersion of crystals having average particle size under 1micron, 5 parts by weight, a phenolic antioxidant/developer (Lowinox44B25, having melting point 210-211° C., available from Chemtura,Middlebury, Conn., coated as an aqueous dispersion of crystals havingaverage particle size under 1 micron, 2 parts by weight), Lowinox 1790(a second phenolic antioxidant/stabilizer, available from Chemtura,Middlebury, Conn., coated as an aqueous dispersion of crystals havingaverage particle size under 1 micron, 0.5 part by weight), a binder(poly(vinyl alcohol, Celvol 540, available from Celanese, Dallas, Tex.,3.2 parts by weight) and glyoxal (0.19 parts by weight). This layer hasa coverage of 2.56 g/m2.

Overlying the magenta color-forming layer 26 is a barrier layer 28 thatcontains a fluorescent brightener. This layer is composed of theabove-mentioned POVAL MP103 (82% by weight), glyoxal (8% by weight) andthe above-mentioned Leucophor BCF P115. This layer has a coverage of 1g/m2.

Overlying the barrier layer 28 is a second thermally-insulatinginterlayer 30 composed of the above-mentioned CP655 (48% by weight), theabove-mentioned CP692 (31% by weight) and the above-mentioned POVALMP103 (21% by weight). This layer has a coverage of 3 g/m2.

Overlying the second thermally-insulating interlayer 30 is a barrierlayer 32 composed the above-mentioned POVAL MP103 (94% by weight) andglyoxal (a crosslinker, 6% by weight). This layer has a coverage of 1g/m2.

Overlying the barrier layer 32 is a yellow color-forming layer 34composed of Dye XI described in U.S. Pat. No. 7,279,264, (59.6% byweight, having melting point 202-203° C.), Lowinox 1790 (a phenolicantioxidant/stabilizer, available from Chemtura, Middlebury, Conn.,coated as an aqueous dispersion of crystals having average particle sizeunder 1 micron, 7.6% by weight), a binder (poly(vinyl alcohol), Celvol540, available from Celanese, Dallas, Tex., 32.8% by weight). This layerhas a coverage of 1.99 g/m2.

Overlying the yellow color-forming layer 34 is a barrier layer 36composed of a fully hydrolyzed poly(vinyl alcohol), Celvol 325,available from Celanese, Dallas, Tex. (94% weight) and glyoxal (6% byweight). This layer has a coverage of 0.5 g/m2.

Deposited on the barrier layer 36 is an ultra-violet blocking layer 38composed of a nanoparticulate grade of titanium dioxide (MS-7, availablefrom Kobo Products Inc., South Plainfield, N.J., 62% by weight), theabove-mentioned POVAL MP103 (35% by weight) and glyoxal (3% by weight).This layer has a coverage of 2 g/m2.

Deposited on the ultra-violet blocking layer 38 is an overcoat 40composed of Carboset 526 (a polymeric binder available from LubrizolAdvanced Materials, Inc., Cleveland, Ohio, 5 parts by weight), theabove-mentioned POVAL MP103 (2.12 parts by weight), NeoRez R-989 (apolyurethane latex, available from DSM NeoResins, Wilmington, Mass.,4.34 parts by weight), Hidorin F-115P (a meltable lubricant, availablefrom Nagase America Corp., New York, N.Y., 5 parts by weight), Pinnacle2530, a grade of erucamide, available from Lubrizol Advanced Materials,Inc., Cleveland, Ohio, (1 part by weight), and Ultraflon AD-10 (apoly(tetrafluoroethylene) lubricant available from Laurel Products LLC,Elverson, Pa., 1.72 parts by weight). This layer has a coverage of 1g/m2.

On the reverse side of substrate 12 is an anticurl layer 42 comprisingabove-mentioned POVAL MP103 (94% by weight) and glyoxal (a crosslinker,6% by weight). This layer has a coverage of 12-15 g/m2 and may contain amatting agent as is well known in the art.

The imaging members described above can be printed using techniques suchas those described in U.S. Pat. No. 6,801,233, U.S. patent applicationSer. No. 11/400,734, filed Apr. 6, 2006, U.S. Pat. No. 7,408,563, andU.S. patent application Ser. No. 12/022,955, entitled “Print HeadPulsing Techniques for Multicolor Printers” of even date herewith.

The invention will now be described further in detail with respect tospecific embodiments by way of Examples, it being understood that theseare intended to be illustrative only and the invention is not limited tothe materials, amounts, procedures and process parameters, etc. recitedherein. All parts and percentages recited are by weight unless otherwisespecified.

Example I Dye 6 a. Preparation of3′-chloro-6′-(4-fluoro-2-methylanilino)fluoran

To a solution of 3′,6′-dichlorofluoran (1107 g, 3.00 mol) in sulfolane(6 L) was added with stirring anhydrous aluminum chloride (1600 g, 12.00mol) at such a rate that the temperature of the batch did not exceed100° C. Upon completion of the addition the reaction mixture wasagitated with passive cooling until the temperature reached 85° C., atwhich point 4-fluoro-2-methylaniline (412.96 g, 3.3 mol) was addeddropwise over 15 minutes, with the reaction being maintained at 85° C.by gentle heating. When this addition was complete, 2,6-lutidine (706.2g, 6.60 mol) was added dropwise over the course of one hour, againmaintaining the temperature at 85° C. At this point HPLC indicated thatthe starting dichlorofluoran had been consumed, so the reaction mixturewas quenched into ice-water (40 liters) with vigorous stirring that wasmaintained for 16 hours. The resulting slurry was filtered and the cakewashed with water (16 L), then sucked dry with a rubber dam. Thestill-damp cake was suspended in acetonitrile (8 L) and heated toreflux, being maintained at this temperature for an additional 15minutes. The suspension, which became quite thick, was allowed to coolto 20° C. and the solid collected by vacuum filtration using a rubberdam. The compacted cake was washed with 2×4 liters of 30% (v/v)acetonitrile/water, dried under a dam, and finally dried in a vacuumoven overnight at 100° C. to provide a pale gray solid weighing 1348 g(98.1% crude yield) suitable for conversion to final dyes.

b. Preparation of3′-(2,4-dimethylanilino)-6′-(4-fluoro-2-methylanilino)fluoran (Dye 6)

A mixture of 3′-chloro-6′-(4-fluoro-2-methylanilino)fluoran (2.0 g; 4.37mmol), 2,4-dimethylaniline (1.10 g; 8.74 mmol), zinc chloride (2.4 g;17.5 mmol), zinc oxide (0.71 g; 8.74 mmol), and sulfolane (10 g) wasstirred with heating at 150° C. overnight. After cooling, the mixturewas quenched into 2N hydrochloric acid (50 mL) to give a precipitatethat was collected by filtration, washed with water, and dissolved intoN,N-dimethylformamide (30 mL). This solution was then neutralized withaqueous ammonium hydroxide (15 mL NH₄OH and 15 mL H₂O) to give aprecipitate that was collected by filtration. This crude product waspurified by column chromatography (eluent: 5% methanol in CH₂Cl₂),followed by recrystallization with a mixture of acetone and hexanes togive 1.66 g white solid (70% yield).

Example II Dye 12 Preparation of3′,6′-bis(4-fluoro-2-methylanilino)fluoran (Dye 12)

A mixture of 3′,6′-dichlorofluoran (19.45 g, mmol),4-fluoro-2-methylaniline (25.0 g, 200 mmol), zinc chloride (22 g, 161mmol), and zinc oxide (6.60 g, 81 mmol) in sulfolane (100 mL) wasstirred at 200° C. for three hours, then cooled to 110° C. over 30 min.The reaction mixture was quenched into a mixture of conc. hydrochloricacid (100 mL) and water (300 mL) to give a red precipitate that wascollected by filtration, washed with water, (150 mL), and suspended inmethanol (200 mL). The suspension was heated to 60° C. and to it wasadded a solution of conc ammonium hydroxide (15 mL) in methanol (20 mL).The solids went completely into solution for a brief time, after whichprecipitation of the presumed free base form of the dye began. Theslurry was stirred with cooling to 20° C. and maintained at thattemperature for 12 hours, then filtered. The cake was washed with coldmethanol (70 mL) and dried in vacuo overnight to give 25.48 g burgandysolid (93% crude yield). Half (12.74 g) of this material was taken up inacetone (40 mL) and diluted with hexanes (90 mL), scratched, and left at5° C. for two days to deposit solid that was collected by filtration andwashed with 25 mL portions of 20%, 10%, 5%, and 0% acetone in hexanes,then dried in vacuo overnight to provide 10.10 g pale purple prisms (79%recovery).

Example III Dye 18 a. Preparation ofN,N-dipropyl-4-methyl-2-nitrobenzamide

To a mixture of 4-methyl-3-nitrobenzoic acid (36.23 g, 0.2 mmol),N,N-dimethylformamide (5 mL), and toluene (85 mL) was added withstirring thionyl chloride (30 mL, 48.8 g, 0.41 mole). The mixture wasstirred at gentle reflux for four hours, then distilled to approximatelyhalf the volume (67.77 g residual net weight) to remove excess thionylchloride. This solution was cooled to 20° C., and 22.6 grams of it(nominally 6.67 mmol) was added to a solution of N,N-di-n-propylamine(22.0 g, 0.22 mole) in ethyl acetate (100 mL) resulting in immediateformation of a slurry that was stirred at ambient temperature overnight.This was then quenched into water (150 mL). The organic layer was washedwith cold 0.5 N hydrochloric acid (100 mL), then with 5% aqueous sodiumbicarbonate, dried (MgSO₄) and evaporated to give a colorless oilweighing 16.55 g (94.0%). This was characterized by proton and carbonnmr, as well as electrospray mass spectrum (M+1 at m/e 265.1).

b. Preparation of N,N-dipropyl-3-amino-4-methylbenzamide

Crude N,N-dipropyl-4-methyl-3-nitrobenzamide (16.35 g, nominally 61.9mmol) was dissolved in ethanol (125 mL). To this solution was added ironpowder (11.34 g, 200 mmol), then, with rapid stirring, was added 12Nhydrochloric acid (42 mL) at such a rate as to maintain a temperature of75° C. (required 10 minutes). The solution was stirred at 75° C. for anadditional 10 minutes, then quenched into water (500 mL). This slurrywas made basic (pH 14) by addition of aqueous potassium hydroxide. Theresulting pudding-like slurry was stirred with ethyl, acetate (300 mL)and filtered (slow). The organic layer of the filtrate was dried (K2CO3)and evaporated to a thick oil that solidified overnight to provide 14.27g (98.5%) of a waxy solid that was characterized by proton nmr.

c. Preparation of3′-chloro-6′-(3-N,N-di-n-propylbenzamido-6-methylanilino)fluoran

To a mixture of 3′,6′-dichlorofluoran (3.69 g; 10.0 mmol) in sulfolane(25 g) was added at 100° C. anh. aluminum chloride (4.0 g, 30 mmol),then, portionwise over 5 min, was addedN,N-dipropyl-3-amino-4-methylbenzamide (2.34 g, 10 mmol). To thismixture, still with stirring at 100° C., was added 2,6-lutidine (2.0 g,18.7 mmol). The mixture was stirred at 110° C. for an additional hour,cooled to 45° C., and quenched into a mixture of ice (100 g) and 6Nhydrochloric acid (120 mL) to give a purple-gray precipitate that wascollected by filtration, washed with cold water (200 mL), and suspendedin dichloromethane (200 mL). This mixture was washed with 5% aqueoussodium bicarbonate (70 mL), then with water (70 mL), and finallyevaporated to a bluish-gray glass, weighing 4.92 g (86.8%), which wascharacterized by proton and carbon nmr.

d. Preparation of3′-(3-N,N-di-n-propylbenzamido-6-methylanilino)-6′-(4-fluoro-2-methylanilino)-fluoran(Dye 18)

To a suspension of3′-chloro-6′-(3-N,N-di-n-propylbenzamido-6-methylanilino)-fluoran (4.40g, 7.7 mmol) and 4-fluoro-2-methylaniline (2.94 g, 23.5 mmol) insulfolane at 90° C. was added anhydrous zinc chloride (5.33 g, 39.1mmol), producing a dark red solution. The temperature was raised to 170°C. and the solution maintained at this temperature for four hours. Themixture was then heated at 185° C. for an additional 1.5 hours, cooledto 120° C., and quenched into cold 1N hydrochloric acid (150 mL) to givea dark red precipitate which was collected by filtration, washed withwater (150 mL), and dried overnight in vacuo at 60° C. to give a darkred solid. This was taken up in dichloromethane (80 mL); to this mixturewas added a solution of 14N ammonium hydroxide (5 mL) in acetone (25mL). The resulting solution was filtered to remove particulates and thenchromatographed (silica gel eluted with dichloromethane, then with 33%,50%, and 75% ethyl acetate). The purest fractions were evaporated togive a pink foam which was crystallized from acetone/hexanes, affording3.67 g (72.7%) of pale pink prisms, mp 228-230.5 C, which werecharacterized by proton and carbon nmr, as well as electrospray massspectrometry (M+1 at m/e 656.3).

Example IV Dye 23 Preparation of3′-(2-fluoroanilino)-6′-(4-fluoro-2-methylanilino)fluoran (dye 23)

Purified 3′-chloro-6′-(4-fluoro-2-methylanilino)fluoran (1.34 kg, 96weight %, 2.82 mol), prepared as described in Example I above) wasdissolved in sulfolane (5 L) at 90-110° C. Zinc chloride (2.0 kg, 14.7mol, 5.2 eq.) was added at 110-130° C., followed by freshly distilled2-fluoroaniline (900 g, 7.08 mol, 2.88 eq.) added at 130-150° C. Theinternal temperature was raised to 190° C. and the reaction stirred atthis temperature for 18 hours. The reaction was cooled to about 100° C.and quenched into a mixture of ice (20 kg), water (10 L) and conc.hydrochloric acid (1000 mL) with vigorous stirring. Agitation wascontinued 18 hours as the mixture attained ambient temperature. Thesolids were filtered and washed with water (2×5 L). The resultant purplesolid was added to ethyl acetate (3 L) and triethylamine (500 mL) undervigorous stirring, which was maintained for an additional 30 min.Heptanes (6 L) was added slowly and the mixture stirred an additional 2hours. The solid was filtered and washed with heptanes/ethyl acetate80/20 (3 L), then with heptanes (3 L). The crude solid was dried at 80°C. for 16 hours to provide ˜1.4 kg of a dark pink solid. The crude dyewas dissolved in THF (3 L) and diluted with toluene (12 L). Silica gel(1 kg) was added and the mixture stirred for 30 minutes, filtered, andwashed with toluene/THF 80/20 (6 L). The volume of the solution wasreduced to 8 L then heptanes (8 L) was added. The slurry was stirred for18 hours, then filtered. The solid was washed with toluene/heptanes 1/1(3 L), then with heptanes (3 L), and finally dried at 80° C. to providethe color-former as a pink solid (1.29 kg, 93%).

Example V Dye 31 a. Preparation of 3′-(2-fluoroanilino)-6′-chlorofluoran

A 500 mL liter flask was charged with sulfolane (150 mL) followed by3′,6′-dichlorofluoran (20 g, 54.17 mmol. 1.0 eq.) and stirredvigorously. Aluminum chloride (22 g, 165 mmole, 3.05 eq.) was added nextin portions to keep the temperature between 85-90° C. 2-Fluoroaniline(15 g, 135 mmole, 2.46 eq.) was added dropwise and the temperature ofthe reaction was kept between 85-90° C. The reaction was allowed to stirfor 30 minutes at temperature (85-90° C.) then poured into ice water(1.5 L) with rapid stirring. The precipitate was collected by vacuumfiltration, and then washed with additional water (1.5 L) until theeluent became colorless. The red solid was dried under vacuum at roomtemperature overnight. The dry solid was dissolved in dichloromethaneand chromatographed on silica gel using heptanes/ethyl acetate from100/0 to 70/30 as an eluent to afford3′-(2-fluoroanilino)-6′-chlorofluoran (20.4 g, 85%) as a white solid.The purity by HPLC was 98.5% by area. The dye was characterized by massspectrometry, DSC-TGA and NMR spectroscopy.

b. Preparation of3′-(4-chloro-2-methylanilino)-6′-(2-fluoroanilino)fluoran (dye 31)

A 250 mL liter flask was charged with sulfolane (75 mL) followed by3′-(2-fluoroanilino)-6′-chlorofluoran (8.0 g, 18.02 mmol. 1.0 eq.) andstirred vigorously. The reaction was heated and zinc chloride (12 g,90.2 mmole, 5.0 eq.) was added in portions when the temperature reached80° C. 4-Chloro-2-methylaniline (8.4 g, 59.3 mmole, 3.3 eq.) was addedin small portions when the temperature reached 120° C. The temperatureof the reaction was increased to 160° C. and the reaction was allowed tostir 18 hours at this temperature. The reaction mixture was then cooledto 100-120° C., then poured into ice water (0.75 L) containing aceticacid (25 mL) with rapid stirring. The precipitate was collected byvacuum filtration, then washed with additional water (1 L) until theeluent became colorless. The red solid was dried under vacuum at roomtemperature overnight. The dry solid was partially dissolved indichloromethane with added triethylamine (most of the product turnedinto a green insoluble form) and chromatographed on silica gel usingheptanes/ethyl acetate from 100/0 to 70/30 as an eluent to afford theproduct (2.58 g, 26%). The solid was slurried in heptanes/acetone 50/50(75 mL) for three hours, filtered, washed with heptanes/acetone 50/50(10 mL) and dried under vacuum at 50° C. to afford3′-(4-chloro-2-methylanilino)-6′-(2-fluoroanilino)fluoran, (1.55 g, 16%)as a pink solid. The purity by HPLC was >99% by area. The dye wascharacterized by mass spectrometry, DSC-TGA and NMR spectroscopy.

Example VI Dye 42 Preparation of 3′,6′-bis(2-fluoroanilino)fluoran (dye42)

To a solution of 3′,6′-dichlorofluoran (37.0 g, 0.10 mole) in sulfolane(200 mL) was added with stirring anhydrous aluminum chloride (40.0 g,0.30 mol). The mixture was heated to 90° C. and 2-fluoroaniline (66.0 g,0.59 mol) was added dropwise with stirring over 5 min. The batch washeld at 170° C. for 5 hours, then cooled to 100 C and quenched into 1000mL 1N hydrochloric acid to give a red precipitate that was collected byfiltration and washed with water (500 mL). The wet cake was suspended inethyl acetate (200 mL) and stirred overnight with triethylamine (20 mL,143 mmol) and water (100 mL). The resulting slurry was filtered and thecake washed with water (150 mL), with ethyl acetate (100 mL), andfinally with 50% ethyl acetate/heptane (100 mL), then dried in vacuoovernight to provide 45.0 g (77%) of pale pink prisms.

Example VII Dye 43 a. Synthesis of3′-(2-Methoxyanilino)-6′-chlorofluoran

A 250 mL liter flask was charged with sulfolane (50 mL) followed by3′,6′-dichlorofluoran (10 g, 27.8 mmol. 1.0 eq.) and the contentsstirred vigorously. Aluminum chloride (9.0 g, 67.5 mmole, 3.0 eq.) wasadded next in portions to keep the temperature between 80-85° C.o-Anisidine (2-methoxyaniline) (5.6 g, 45.5 mmole, 1.63 eq.) was addeddropwise and the temperature of the reaction was kept between 80-85° C.The reaction was allowed to stir for 30 minutes at temperature (80-85°C.) then poured into ice water (1 L) with rapid stirring. Theprecipitate was collected by vacuum filtration, and then washed withadditional water (1 L) until the eluent became colorless. The purplesolid was dried under vacuum at room temperature overnight. The drysolid was dissolved in dichloromethane with added triethylamine andchromatographed on silica gel using heptanes/ethyl acetate from 100/0 to70/30 as an eluent to afford 3′-(2-methoxyanilino)-6′-chlorofluoran(15.7 g, 64%) as a white solid. The purity by HPLC was >99% by area. Thedye was characterized by mass spectrometry, DSC-TGA, and NMRspectroscopy.

b. Synthesis of[3′-(2-methoxyanilino)-6′-(2-fluoro-4-methylanilino)fluoran] (dye 43)

To a 250 mL liter flask was added sulfolane (50 mL) followed by3′-(2-methoxyanilino)-6′-chlorofluoran (6.0 g, 13.16 mmol. 1.0 eq.), andN,N′,N′,N″,N″-pentamethyldiethylenetriamine (1.75 g, 10.1 mmol, 0.77eq.). The mixture was stirred vigorously. The reaction was heated andzinc chloride (8.0 g, 58.8 mmole, 4.46 eq.) was added in portions whenthe temperature reached 80° C. 2-Fluoro-4-methylaniline (2.5 g, 19.98mmole, 1.52 eq.) was added in small portions when the temperaturereached 120° C. The temperature of the reaction was increased to 170° C.and the reaction was allowed to stir 18 hours at this temperature. Thereaction mixture was then cooled to 100-120° C. then poured into amixture of ice water (0.75 L) and acetic acid (25 mL) with rapidstirring. The precipitate was collected by vacuum filtration, and thenwashed with additional water (1 L) until the eluent became colorless.The red solid was dried under vacuum at room temperature overnight. Thedry solid was partially, dissolved in dichloromethane with addedtriethylamine (some of the product turns into a green form) andchromatographed on silica gel using heptanes/ethyl acetate from 100/0 to60/40 as an eluent to afford the product (4.3 g, 60%). The solid wascrystallized from heptanes/acetone 90/10 (75 mL) overnight, filtered,washed with heptanes/acetone 90/10 (20 mL), then heptanes (20 mL), anddried under vacuum at 50° C. to afford3′-(2-methoxyanilino)-6′-(2-fluoro-4-methylanilino)fluoran (2.2 g, 31%)as a pink solid. The purity by HPLC was >99% by area. The dye wascharacterized by mass spectrometry, DSC-TGA and NMR spectroscopy.

Example VIII Dye 45 a. Synthesis of3′-(2-ethoxyanilino)-6′-chlorofluoran

To a 500 mL liter flask was added sulfolane (150 mL) followed by3′,6′-dichlorofluoran (20 g, 54.17 mmol. 1.0 eq.) with vigorousstirring. Aluminum chloride (22 g, 165 mmole, 3.05 eq.) was added nextin portions to keep the temperature between 80-85° C. o-Phenetidine(2-ethoxyaniline) (16 g, 116.6 mmole, 2.15 eq.) was added dropwise andthe temperature of the reaction was kept between 80-85° C. The reactionwas allowed to stir for 30 minutes at temperature (80-85° C.), thenpoured into ice water (1.5 L) with rapid stirring. The precipitate wascollected by vacuum filtration, and washed with additional water (1.5 L)until the eluent became colorless. The red solid was dried under vacuumat room temperature overnight. The dry solid was dissolveddichloromethane with added triethylamine and chromatographed on silicagel using heptanes/ethyl acetate from 100/0 to 70/30 as an eluent toafford 3′-(2-ethoxyanilino)-6′-chlorofluoran (20.6 g, 81%) as a whitesolid. The purity by HPLC was >99% by area. The dye was characterized bymass spectrometry, DSC-TGA and NMR spectroscopy.

b. Preparation of3′-(2-ethoxyanilino)-6′-(2-fluoro-4-methylanilino)fluoran (dye 45)

To a 250 mL liter flask was added sulfolane (60 mL) followed by3′-(2-ethoxyanilino)-6′-chlorofluoran (7.0 g, 14.9 mmol. 1.0 eq.) withvigorous stirring. The reaction was heated and zinc chloride (10.5 g,77.0 mmole, 5.17 eq.) was added in portions when the temperature reached80° C. 2-Fluoro-4-methylaniline (6.25 g, 49.9 mmole, 3.35 eq.) was addedin small portions when the temperature reached 120° C. The temperatureof the reaction was increased to 170° C. and the reaction was allowed tostir 18 hours at this temperature. The reaction mixture was then cooledto 100-120° C. then poured into ice water (0.75 L) and acetic acid (25mL) with rapid stirring. The precipitate was collected by vacuumfiltration, then washed with additional water (1 L) until the eluentbecame colorless. The red solid was dried under vacuum at roomtemperature overnight. The dry solid was dissolved in dichloromethanewith added triethylamine and chromatographed on silica gel usingheptanes/ethyl acetate from 100/0 to 40/60 as an eluent to afford theproduct (3.4 g, 41%). The solid was crystallized from heptanes/acetone90/10 (75 mL) overnight, filtered, washed with heptanes/acetone 90/10(20 mL) then heptanes (20 ml) and dried under vacuum at 50° C. to afford3′-(2-ethoxyanilino)-6′-(2-fluoro-4-methylanilino)fluoran (2.47 g, 30%)as a pink solid. The purity by HPLC was >99% by area. The dye wascharacterized by mass spectrometry, DSC-TGA and NMR spectroscopy.

Example IX Light Stability of Crystals

This example illustrates the improved photostability of coatings ofcolorless crystals of compounds of the present invention as compared toa representative compound of the prior art. Coatings were prepared asfollows:

a. Preparation of a Dispersion of Crystals of the Color-Former:

A glass jar (1 oz size) containing zirconium oxide grinding beads (10 g)was charged with crystals of the color-former under test (2.0 g), asolution of poly(vinyl alcohol) (Elvanol 4016, available from DuPontCorporation, Wilmington, Del., 3.0 g of a 6.7% aqueous solution),deionized water (4.5 g), and methyl acetate (1.0 g), and the mixture wasstirred magnetically for 18-24 hours to produce a fine dispersion.

b. Preparation of Coating Fluid.

The dispersion prepared as described in a. above (3.5 g) was combinedwith poly(vinyl alcohol) (Celvol 205, available from Celvol 205,available from Celanese, Dallas, Tex., 0.98°g of a 12.3% aqueoussolution), Zonyl FSN (a coating aid, available from Dupont, Wilmington,Del., 0.045 g), Zonyl FSA (a coating aid, available from Dupont,Wilmington, Del., 0.045 g), glyoxal (a crosslinker, 0.15 g of a 5%aqueous solution) and deionized water (3.43 g).

c. Preparation of Coating.

The fluid prepared as described in b. above was coated onto a white,filled poly(ethyleneterephthalate) (PET) film base of 3 mil thickness(Melinex 339, available form Dupont Teijin films, Hopewell, Va.) thathad been subcoated with poly(vinyl alcohol) (Celvol 325, available fromCelanese, Dallas, Tex., 1 g/m²) using a #10 Mayer rod to give a driedcoating thickness of approximately 0.3 g/m² of the color-former.

This procedure was followed using four color-forming materials of thepresent invention as well as a control color-forming material (Dye IV ofcopending U.S. patent application Ser. No. 11/433,808, comprising anoctyl grouping on one of the nitrogen atoms bonded to the xanthenenucleus).

The coatings so formed were exposed to fluorescent lighting (2500 ft.candles) in an oxygen atmosphere, and the time taken for the reflectionoptical density to rise 0.05 above its initial value (measured in days)was recorded. The results of this test are reproduced in Table III,below.

TABLE III Time (days) Control 0.51 Dye 23 3.58 Dye 31 1.08 Dye 36 1.24Dye 42 1.55 Dye 44 1.73

It can be seen that the photostability of the colorless crystalline formof the materials of the present invention is substantially superior tothat of the control material. The best performance as measured in thistest was that of Dye 23 of the present invention.

Although the invention has been described in detail with respect tovarious preferred embodiments, the present disclosure is not to belimited in terms of the particular embodiments described in thisapplication. Many modifications and variations can be made withoutdeparting from its spirit and scope, as will be apparent to thoseskilled in the art. Functionally equivalent methods and apparatuseswithin the scope of the disclosure, in addition to those enumeratedherein, will be apparent to those skilled in the art from the foregoingdescriptions. Such modifications and variations are intended to fallwithin the scope of the appended claims. The present disclosure is to belimited only by the terms of the appended claims, along with the fullscope of equivalents to which such claims are entitled. It is to beunderstood that this disclosure is not limited to particular methods,reagents, compounds compositions or biological systems, which can, ofcourse, vary. It is also to be understood that the terminology usedherein is for the purpose of describing particular embodiments only, andis not intended to be limiting.

In addition, where features or aspects of the disclosure are describedin terms of Markush groups, those skilled in the art will recognizethat, the disclosure is also thereby described in terms of anyindividual member or subgroup of members of the Markush group.

As will be understood by one skilled in the art, for any and allpurposes, particularly in terms of providing a written description, allranges disclosed herein also encompass any and all possible subrangesand combinations of subranges thereof. Any listed range can be easilyrecognized as sufficiently describing and enabling the same range beingbroken down into at least equal halves, thirds, quarters, fifths,tenths, etc. As a non-limiting example, each range discussed herein canbe readily broken down into a lower third, middle third and upper third,etc. As will also be understood by one skilled in the art all languagesuch as “up to,” “at least,” “greater than,” “less than,” and the likeinclude the number recited and refer to ranges which can be subsequentlybroken down into subranges as discussed above. Finally, as will beunderstood by one skilled in the art, a range includes each individualmember.

While various aspects and embodiments have been disclosed herein, otheraspects and embodiments will be apparent to those skilled in the art.The various aspects and embodiments disclosed herein are for purposes ofillustration and are not intended to be limiting, with the true scopeand spirit being indicated by the following claims.

All publications, patent applications, issued patents and otherdocuments referred to in this specification are herein incorporated byreference as if each individual publication, patent application, issuedpatent, or other document was specifically and individually indicated tobe incorporated by reference in its entirety. Definitions that arecontained in text incorporated by reference are excluded to the extentthat they contradict definitions in this disclosure.

1. A compound represented by the formula (I):

wherein: R₁-R₁₀ are alkyl or hydrogen; at least one of R₁₁, R₁₅, R₁₆ andR₂₀ is alkyl or halogen; at least one of R₁₁, R₁₃, R₁₅, R₁₆, R₁₈ and R₂₀is fluorine; and R₁₁-R₂₀ are chosen from the group consisting ofhydrogen, alkyl, substituted alkyl, halogen, alkoxy, and substitutedcarbonyl. 2-13. (canceled)